If you changed your state of residence from Maryland to South Carolina and received the distribution while a resident of South Carolina, then all of the distribution is attributed to (i.e. taxed by) South Carolina. Retirement distributions (early or normal) are "retirement income" and are taxed by your state of residence at the time of the distribution.
Effective
for retirement income received after December 31, 1995, federal law prohibits
any state from taxing certain retirement income (mainly pension income) unless
you are resident of, or domiciled in, that state. For example, if you receive a
pension from your former California employer and you now reside in New Mexico,
California may not tax your retirement income. Because you are now a New
Mexico resident, your retirement income is taxable in New Mexico.
